The invention relates generally to escapement mechanisms and deals more particularly with an escapement mechanism which is very reliable and operable with a single actuator.
Escapement mechanisms of the type with which this invention is concerned are commonly used to advance or index a leading one of a row of gravity biased objects such as food items or mechanical parts supported on a guide. They are also used to controllably advance workpiece carrying trolleys in conveyorized transport systems such as the one disclosed in co-pending U.S. patent application, Ser. No. 683,379, filed 12-19-84 by Osthus and Nymark, assigned to the assignee of the present invention and hereby incorporated by reference as part of the present disclosure.
The aforesaid conveyorized transport system is highly automated and includes a rail network for carrying the trolleys, a propulsion track for propelling the trolleys, and switches for routing the trolleys within the rail network. The rail network comprises a main rail and subsidiary loop rails, the main rail guides the trolleys to and from the subsidiary loop rails, and the subsidiary loop rails guide then to and from work stations. The propulsion track is located adjacent the main rail and includes an endless moving chain and pushers attached thereto, which pushers engage the trolleys to propel them along the main rail. The switches are computer controlled and are located between the main rail and the subsidiary loop rails to transfer the trolleys to and from the subsidiary loops as indicated by a computer program tape.
Each subsidiary loop rail slopes continuously downwardly from where the trolleys are taken from the main rail, and eventually joins with an elevator which reloads the trolleys onto the main rail so that the trolleys move along the subsidiary loop rail by gravity. A trolley stop is located approximately midway around the subsidiary loop rail adjacent the work station, which trolley stop comprises an escapement mechanism at its upstream end and a gate at its downstream end. The escapement mechanism backs up the trolleys on the subsidiary loop rail to await attention by an operator, and when activated, it releases a leading one of the trolleys which then rolls by gravity to the gate where it is isolated form the other trolleys and the workpieces it carries are freely accessible to the operator. The operator then may perform a work operation on the accessible workpieces, and when completed, activate the gate to release the trolley to roll by gravity towards the elevator and activate the escapement mechanism to release another trolley carrying fresh workpieces to the gate. Another escapement mechanism is located at the base of the elevator to release the trolleys one by one for loading onto it.
Both escapement mechanisms of the aforesaid patent application comprise a leading piston and cylinder assembly and a trailing piston and cylinder assembly mounted parallel to one another, adjacent the subsidiary loop rail such that the piston rods of the assemblies are extendable to cross the subsidiary loop rail into the path of the trolleys. The piston rods are spaced from each other by a few inches corresponding to the linear displacement of each trolley, and in the rest condition, the leading piston rod is extended to back up the trolleys and the trailing piston rod is retracted. Then, when the escapement mechanism is activated, the trailing piston rod is extended between the trolley presently first in line and the one behind it and the leading piston rod is retracted to allow the leading trolley to roll by gravity towards the downstream gate and to allow the remaining trolleys to advance slightly to the trailing piston rod. After the leading trolley advances past the leading piston rod, the leading piston rod is extended and the trailing piston rod is retracted to allow the remaining trolleys to advance to the leading piston rod. It is usually required that the leading piston rod be retracted shortly after the trailing piston rod is extended; otherwise all the trolleys may advance slightly during a short period when the ends of both piston rods pass each other and are out of the path of the trolleys and the trolley second in line moves into the path of the trailing piston rod jamming it.
There are at least two ways to control the timing of the extension and retraction of the piston rods of the piston and cylinder assemblies within the aforesaid escapement mechanism. Two solenoids may be used to independently control the assemblies but this complicates the control system, or both assemblies may be connected in parallel and a single solenoid used for both assemblies, provided a suitable delaying mechanism, such as a flow valve, is installed between the solenoid and the leading piston and cylinder assembly. By appropriate energization of the solenoid, the trailing piston rod is first extended between the leading trolley and the next in line, but because of the delaying mechanism, the leading piston rod is not fully retracted until a short time later. The flow valve plays little role in the deactivation of the piston and cylinder assemblies because of internal bias springs, and after the leading trolley advances past the leading piston rod, both piston and cylinder assemblies are de-activated so both piston rods return to their rest position approximately simultaneously. The flow valve within the escapement mechanism is difficult to adjust to provide the necessary delay between the extension of the trailing piston and the retraction of the leading piston and requires periodic maintenance.
The gate comprises another piston and cylinder assembly having a piston rod which is extendable to cross the subsidiary loop rail in the path of the released trolley. The solenoid which activates the escapement mechanism of the stop can also be used to control the piston and cylinder assembly of the gate in synchronism with the leading piston and cylinder assembly of the escapement mechanism provided that the time between the retraction of the leading piston rod and its re-extension is less than the time it takes for the trolley to roll from the escapement mechanism to the gate so that the trolley does not bypass the gate.
In addition to the difficulty in adjusting the flow valve, there is another problem with the aforesaid escapement mechanism. When a number of trolleys are backed up against either piston rod, the weight of the trolleys exerts a sizable bending moment on the rod, which moment may jam the piston and cylinder assembly.
Accordingly, a general aim of the invention is to provide a very reliable escapement mechanism.
A more specific aim of the invention is to provide an escapement mechanism which is operable with a single actuator, simple to operate and rarely in need of adjustment.